1. Field of the Invention
The present invention relates to a pulse radar apparatus. More particularly, the invention relates to a pulse radar apparatus for transmitting an electric wave to receive the reflected electric wave into which the transmitted electric wave is reflected by an object, thereby detecting the presence or absence of the object to measure a distance up to the detected object.
2. Description of the Related Art
FIG. 15 shows a schematic configuration of a conventional pulse radar apparatus, which is described, for example, in Japanese Patent Laid-open No. 7-72237. In the figure, reference numeral 1501 designates a pulse signal sending unit for outputting a pulse signal to a target; reference numeral 1502 designates a control unit for carrying out the control of the operation of the pulse radar apparatus; reference numeral 1503 designates a reflected pulse signal receiving unit for receiving a reflected pulse into which the pulse signal outputted from the sending unit 1501 is reflected by the target to be returned back; reference numeral 1504 designates a sampling unit for sampling a binary-coded signal every predetermined sampling point to obtain a sampling value of 0 or 1; reference numeral 1505 designates a plurality of addition/storage units for adding the sampling value of 0 or 1, which has been sampled by the sampling unit 1504, every predetermined number of times of sending of the sending unit 1501; and reference numeral 1506 designates a judgement unit for on the basis of the addition result provided by the addition/storage unit 1505, judging whether or not a reflected pulse from a target is present.
Next, the description will hereinbelow be given with respect to the operation of the pulse radar apparatus shown in FIG. 15. In the conventional pulse radar apparatus shown in FIG. 15, a pulse-like signal is periodically outputted by the pulse signal sending unit 1501. Then, the reflected pulses from a target (not shown) are continuously received by the receiving unit 1503 so as to be binary-coded. Then, the sampling unit 1504 samples the binary-coded signal every fixed one sampling point or a plurality of fixed sampling points after the sending timing of the sending unit 1501 to obtain the sampled value of 0 or 1 to supply the sampled value to the addition/storage units 1505 corresponding to the sampling points. Then, the addition/storage unit 1505 adds the sampled values of 0s or 1s every predetermined number of times of sending of the signals by the sending unit 1501. After completion of the addition processing for the predetermined number of times, the judgement unit 1506 compares the normalized addition value which has been obtained by dividing the addition value every addition/storage unit 1505 by the number of times of the addition with a predetermined threshold value to judge on the basis of the comparison result whether or not the reflected pulse signal from the external target is present to judge on the basis of this judgement result whether or not the external target is present.
However, in the above-mentioned conventional pulse radar apparatus, the isolation for the transmission and the reception is poor. When the so-called leakage waveform is present, it is difficult from the following reason to carry out the detection of an object which is a distance smaller than 10 m away from the apparatus, and to carry out the measurement of the distance when the object is present by using the above-mentioned conventional apparatus. That is, in the case of the conventional pulse radar apparatus, since the transmission pulse width is 66.7 ns corresponding to 10 m in terms of the distance, when an object is a distance smaller than 10 m away from the apparatus, the waveform as shown in FIG. 14 in which the leakage waveform and the waveform of the reflected electric wave overlap each other is detected. For this reason, if the threshold value is set on the basis of the reception level during non-transmission, i.e., the so-called noise level, then there arises a problem in that only the leading part of the leakage waveform can not be detected, and it is impossible to detect the leading part of the reflected electric wave which is wanted to be really detected.
In order to cope with such a problem, there have been proposed a method in which the pulse width is made very short, e.g., 350 ps as described in an article of W. Weidmann and D. Steinbuch, xe2x80x9cHigh Resolution Radar for Short Range Automotive Applicationsxe2x80x9d, 28-th European Microwave Conference Amsterdam, 1998, and a method in which the leakage waveform is cancelled by utilizing the transmission waveform as described in Japanese Patent Laid-open No. 10-62518. However, if the transmission pulse width is shortened down to 350 ps as described in the above-mentioned article, since the leakage waveform and the waveform of the reflected electric wave overlap each other only when the distance up to the object is equal to or smaller than 5 cm, the above-mentioned problem is solved. However, there arises a problem in that since the occupation bandwidth thereof becomes very wide, such an apparatus can not be used under the scope of the current Electric Wave Law. In addition, in the case where the leakage waveform is cancelled by utilizing the transmission waveform as described in Japanese Patent Laid-open No. 10-62518, there arises a problem in that it is difficult to cope with the difference or the like in the time interval ranging from the transmission to the reception of the leakage waveform due to the difference in the object.
In the light of the foregoing, the present invention has been made in order to solve the above-mentioned problems associated with the prior art, and it is therefore an object of the present invention to provide a pulse radar apparatus which is capable of detecting properly an object, which is a short distance away from the apparatus, to measure a distance up to the object even if a leakage signal is contained in a received signal.
In view of the above object, a pulse radar apparatus of the present invention, comprises: transmission means for transmitting an electric wave; reception means for receiving the reflected electric wave into which the electric wave transmitted by said transmission means has been reflected by an object to output the received signal thereof; waveform leading part extracting means for extracting a plurality of leading parts of the received signal outputted by said reception means; time interval measuring means for on the basis of the extraction result provided by said waveform leading part extracting means, measuring a time interval ranging from the transmission to the reception by said transmission means; and detection/distance measuring means for judging on the basis of the time interval data outputted by said time interval measuring means whether or not an object is present and when an object is present, calculating the distance up to the object.
Alternatively, a pulse radar apparatus of the present invention may comprise: transmission means for transmitting an electric wave; reception means for receiving the reflected electric wave into which the electric wave transmitted by said transmission means has been reflected by an object to output the received signal thereof; waveform leading part extracting means for extracting a plurality of leading parts of the received signal outputted by said reception means; sampling means for sampling the output of said waveform leading part extracting means at predetermined time intervals; addition means for adding and storing the output result of said sampling means every sampling timing; and detection/distance measuring means for on the basis of the addition result for each of the sampling timings outputted by said addition means, judging whether or not an object is present and when an object is present, calculating a distance up to the object.